Magnetic resonance technology is a known technology for, among other things, obtaining images of the inside of a body of an examination subject. In a magnetic resonance device (MR device), rapidly switched magnetic gradient fields which are generated by means of gradient coils are superimposed on a static main magnetic field B0 which is generated by a main field magnet. In order to emit magnetic resonance signals, the magnetic resonance device comprises further a high-frequency antenna (HF antenna) which irradiates the examination subject with HF signals, the so-called B1 field. With the aid of this antenna or further local antennas, the emitted magnetic resonance signals can be recorded and processed into magnetic resonance images. The B1 field and the HF field are generally generated by currents through a conductor.
From U.S. Pat. No. 6,433,550, for example, an open magnetic resonance device having a C-shaped main field magnet is known which comprises at each of the two ends of the C structure on either side of a space for accommodating a patient, said space being arranged in the opening of the C structure of the magnetic resonance device, pole pieces between which the main magnetic field of the magnetic resonance device can be generated at least inside the space for accommodating a patient. Furthermore, there are arranged on each of the pole pieces, on the sides facing the space for accommodating a patient, parts, fashioned essentially planarly, of a gradient coil system and, adjacent thereto, parts, also essentially planarly fashioned, of an antenna system of the magnetic resonance de vice. Gradient coils for the above-mentioned gradient coil system are described in detail for example in DE 40 37 894 A1 and DE 44 22 781 C1.
Furthermore, from DE 42 32 884 A1 an antenna arrangement for a nuclear-magnetic resonance device is known in which a main magnetic field is established between two pole pieces. A sub-antenna into which a high-frequency current is fed is arranged on each pole piece. The sub-antennas consist of a closed, grounded shield facing the respective pole piece and a planar conductor structure arranged at a distance from, and essentially parallel to, the shield.
Furthermore, it is known from DE 42 32 884 A1 that the objective in the case of pole—piece main field magnets is to keep the distance between the pole pieces as small as possible so that the weight of the main field magnet remains small and better homogeneity of the main magnetic field is achieved. For this reason, it is advantageous to keep all components accommodated between the pole pieces such as the gradient coil system, the high-frequency shield and the antenna arrangement, as flat as possible. On the other hand, for the described antenna arrangement to have a high level of efficiency, the maximum possible gap between the antenna arrangement and the high-frequency shield is advantageous. This applies in particular where the antenna arrangement is used for receiving magnetic resonance signals.
A circular planar high-frequency antenna for open magnetic resonance devices is known from DE 101 24 737 A1. It has two spaced systems of planar conductors, arranged on a mounting plate, for currents crossing one another. The conductors are capacitatively shortened at at least one end to tune to the desired resonance frequency by means of tuning capacitors connected to ground. There is arranged on each mounting plate only one planar metal layer into which, shifted through 90°, the two currents, which are in turn by 90° out of phase, are fed. Tuning capacitors are arranged at the infeed point and on the opposite side.